Computer Organisation | One bit memory cell

One Bit memory cell is also called Basic Bistable element. It has two cross-coupled inverters, 2 outputs Q and Q’. It is called “Bistable” as the basic bistable element circuit has two stable states logic 0 and logic 1.

The following diagram shows the Basic Bistable element:

(A) when A=0,
(i) In inverter1, Q = A'= B= 1
(ii)In inverter2, Q' = B' = A = 0

(B) when A=1,
(i) In inverter1, Q = A'= B= 0
(ii)In inverter2, Q' = B' = A = 1 

Some key points:

  1. The 2 outputs are always complementary.
  2. The circuit has 2 stable states. when Q=1, it is Set state. when Q=0, it is Reset state.
  3. The circuit can store 1-bit of digital information and so it is called one-bit memory cell.
  4. The one-bit information stored in the circuit is locked or latched in the circuit. This circuit is also called Latch.

One-bit six transistor SRAM memory cell is volatile. Fast switching speed is its main advantage. It needs a constant power supply because of its volatility. The demand for faster and denser memory devices has seen memristors being proposed as replacements for flash memory, Static Random Access Memory (SRAM) and Random Access Memory (RAM). The most salient feature of memristors is its resistive switching ability that can retain resistance states for long periods despite without power supply.



The One-bit non-volatile memory cell can be designed using transmission gates and memristor. Memristive devices have high switching speed, low energy consumption, non-volatile and small device size. The non-volatility of memristor used in designs as the information storage element provides retention ability of up to 10 years in the absence of power supply. The transmission gates used ensures that voltage is not lost through other components of the memory cell, thus improves the switching speed by providing a larger potential difference across the memristor.

Other advantages of using memristors in memory devices are its long retention period, excellent endurance properties, and good scalability compared to NAND-based flash memory devices.

Reference:
DIGITAL ELECTRONICS – Atul P. Godse, Mrs. Deepali A. Godse
IEEE XPLORE, Digital library – One-bit non-volatile memory cell using memristor and transmission gates.



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